This invention relates to a thickened aqueous hydrochloric acid compositions and to their use as lime scale removers or in acid treatment of subterranean formations surrounding oil or gas wells.
Aqueous hydrochloric acid compositions are known as lime scale removers, e.g., for use in domestic and institutional applications. French Patent Application Publication No. 2,207,984 discloses the use of a tertiary amine ethoxylate as a thickener in such compositions.
Use of aqueous hydrochloric acid compositions in acid treatment of subterranean formations surrounding oil or gas wells, to increase fluid permeability of the formations, is also known. Such composition are generally used in carbonate formations such as limestone or dolomite, and may be employed in acid fracturing or in matrix acidizing techniques. In acid fracturing, acid is injected at a pressure sufficient to cause the formation to rupture, thereby creating a fracture extending a relatively long distance from the well. Conductive channels are then formed by acid etching of the carbonate fracture walls. Matrix acidizing is effected by injection of acid at lower pressures so that fracturing does not occur. The acid attacks the carbonate formation and etches channels which radiate outwardly from the well. Such channels are commonly referred to as wormholes. The use of hydrochloric acid compositions in such techniques is disclosed in for example U.S. Pat. Nos. 3,734,186, 3,353,603, 3,831,679 and 4,073,344.
Thickened aqueous hydrochloric acid compositions particularly suitable for external cleaning of vehicles such as railroad rolling stock are described in U.S. Pat. No. 3,793,221. These aqueous compositions comprise hydrogen chloride, an organic acid (one or more of oxalic, tartaric and citric acids), a non-ionic surfactant and an anionic surfactant. Inter alia the non-ionic surfactant may be an alkylene oxide adduct of a higher aliphatic alcohol. Linear alkylbenzene sulfonic acids are preferred anionic surfactants. It is stated to be critical to the success of the compositions that the non-ionic portion of the total surfactant be from about 75 to about 95 weight percent.
Desirable properties in a thickened aqueous hydrochloric acid composition for use in acid treatment of subterranean formations surrounding oil or gas wells include: viscosity to decrease at higher rates of shear (must not exhibit Weissenberg effect), viscosity to be low when acid is spent, and stability of the acid composition to be good.
There has now been discovered, a relatively narrow class of thickened hydrochloric acid compositions exhibiting particularly desirable properties.
According to the present invention therefore there is provided a thickened aqueous hydrochloric acid composition comprising:
(a) 1 to 20 percent by weight (%w) hydrogen chloride, PA1 (b) an alcohol ethoxylate of the formula EQU R--O--CH.sub.2 --CH.sub.2 --O).sub.n H (I) PA1 wherein R is a C.sub.8-20 alkyl group and n has an average value in the range 3 to 15, provided that the (CH.sub.2 --CH.sub.2 --O).sub.n moiety constituents 50 to 67%w of the alcohol ethoxylate, PA1 (c) an alkyl aryl sulfonic acid of the formula ##STR3## wherein R.sup.1 is a C.sub.8-13 linear alkyl chain and R.sup.2 and R.sup.3 are independently hydrogen atoms or methyl groups, the combined concentration of (b) and (c) being in the range 3 to 15%w, the relative weight proportions of (b) and (c) being in the range 45 to 65% of (b) to 55 to 35% of (c), and PA1 (d) 0 to 2%w of a salicylate of the formula ##STR4## where R.sup.4 is a C.sub.1-14 alkyl or a benzyl group.
Preferably the composition comprises at least 2%w, advantageously at least 5%w hydrogen chloride; 5 to 15%w hydrogen chloride is particularly preferred, 10 to 15%w hydrogen chloride being most preferred.
It is preferred for R to be a C.sub.8-18 alkyl group.
Those skilled in the art will appreciate that due to commercial methods of production there may be a degree of unsaturation associated with the alkyl groups R and R.sup.1 in the compounds of formula I and/or II, and there may be branching in the R.sup.1 group in a minor proportion of the compound of formula II.
The combined concentration of (b) and (c) is preferably in the range 5 to 12%w.
Inclusion of small quantities of a salicylate of the above general formula have been found to confer increased viscosity upon compositions of the invention. Accordingly if a composition of a specified desired viscosity is to be prepared it may be commercially advantageous in some cases to include a quantity, e.g., between about 0.1 and 2.0%w, of a salicylate. The combined concentration of (b) and (c) may then typically be reduced without disadvantage. Preferably the salicylate will be present in an amount ranging from 0.25 to 1%w, conveniently about 0.5%w.
The salicylate may suitably, but not necessarily, be methyl, ethyl or benzyl salicylate. Methyl salicylate has been found to be very effective.
Compositions according to the invention may be prepared, for instance, by mixing the alcohol ethoxylate and the alkyl benzene sulfonic acid and dispersing the resulting blend, together with the salicylate when present, in aqueous hydrochloric acid. If desired the alkyl benzene sulfonic acid may be added in salt form, e.g., as the sodium sulfonate, and it will be appreciated that in the resulting composition it will be in the form of the acid.
Depending on the eventual desired use, the compositions may contain an additional component or components such as dyes, perfumes, germicides, sulfuric acid or phosphoric acid.
The invention further includes the use of a composition of the invention as a lime scale remover, e.g., for use in domestic and institutional applications such as cleaning of sanitary apparatus (e.g., lavatories, wash basins and baths), ceramic tiled surfaces, dishwashers and washing machines, or in acid treatment of subterranean formations surrounding oil or gas wells. In acid treatment of subterranean formations, the alcohol ethoxylate, alkyl benzene sulfonic acid and, when used, the salicylate may be added to the hydrochloric acid by means of an in-line blender.